CORRELATION OF ENVIRONMENT AND PHYLOGENY WITH THE EXPRESSION OF BETA-HYDROXYBUTYRATE DEHYDROGENASE IN THE MOLLUSCA

The enzyme beta-hydroxybutyrate catalyzes the interconversion of the k etone bodies, acetoacetate and beta-hydroxybutyrate. Although the acti vity of beta-hydroxybutyrate dehydrogenase is relatively high in fresh water and terrestrial molluscs, it is undetectable in all marine mollu scs examined. We tested the effects of conditions of tissue preparatio n and ionic strength of assay media on the measurement of beta-hydroxy butyrate dehydrogenase and conclude that the apparent absence of this enzyme in marine molluscs is not an artifact of conditions of measurem ent. Measurements of other enzymes involved in ketone body and lipid m etabolism in the hepatopancreas of the marine snail Littorina littoria , the freshwater snail Stagnicola elodes and the terrestrial snail Cep aea nemoralis suggest that the differential expression of the enzyme m ay be related to differences in the metabolic organization of marine m olluscs and their freshwater and terrestrial counterparts. Mapping of the presence/absence of beta-hydroxybutyrate dehydrogenase onto a biva lve and gastropod phylogeny indicates four independent occurrences of the enzyme.